you probably log in and out of a half dozen remote servers (or these days, local virtual machines) on a daily basis. And if you’re even more like me, you have trouble remembering all of the various usernames, remote addresses and command line options for things like specifying a non-standard connection port or forwarding local ports to the remote machine.

Shell Aliases

Let’s say that you have a remote server named dev.example.com, which hasnot been set up with public/private keys for password-less logins. The username to the remote account is fooey, and to reduce the number of scripted login attempts, you’ve decided to change the default SSH port to 2200 from the normal default of 22. This means that a typical command would look like:

$ ssh fooey@dev.example.com -p 22000password: *************

Not too bad.

We can make things simpler and more secure by using a public/private key pair; I highly recommend using ssh-copy-id for moving your public keys around. It will save you quite a few folder/file permission headaches.

~/.ssh/config

This means that I can simply $ ssh dev, and the options will be read from the configuration file. Easy peasy. Let’s see what else we can do with just a few simple configuration directives.

Personally, I use quite a few public/private keypairs for the various servers and services that I use, to ensure that in the event of having one of my keys compromised the dammage is as restricted as possible. For example, I have a key that I use uniquely for my github account. Let’s set it up so that that particular private key is used for all my github-related operations:

Host dev HostName dev.example.com Port 22000 User fooey

Host github.com IdentityFile ~/.ssh/github.key

The use of IdentityFile allows me to specify exactly which private key I wish to use for authentification with the given host. You can, of course, simply specify this as a command line option for “normal” connections:

$ ssh -i ~/.ssh/blah.key username@host.com

but the use of a config file with IdentityFile is pretty much your only optionif you want to specify which identity to use for any git commands. This also opens up the very interesting concept of further segmenting your github keys on something like a per-project or per-organization basis:

Which means that if I want to clone a repository using my organization credentials, I would use the following:

$ git clone git@github-org:orgname/some_repository.git

Going further

As any security-conscious developer would do, I set up firewalls on all of my servers and make them as restrictive as possible; in many cases, this means that the only ports that I leave open are 80/443 (for webservers), and port 22 for SSH (or whatever I might have remapped it to for obfuscation purposes). On the surface, this seems to prevent me from using things like a desktop MySQL GUI client, which expect port 3306 to be open and accessible on the remote server in question. The informed reader will note, however, that a simple local port forward can save you:

This will forward all local port 9906 traffic to port 3306 on the remotedev.example.com server, letting me point my desktop GUI to localhost (127.0.0.1:9906) and have it behave exactly as if I had exposed port 3306 on the remote server and connected directly to it.

Now I don’t know about you, but remembering that sequence of flags and options for SSH can be a complete pain. Luckily, our config file can help alleviate that:

And my local port forwarding will be enabled using all of the configuration directives I set up for the tunnel host. Slick.

Homework

There are quite a few configuration options that you can specify in~/.ssh/config, and I highly suggest consulting the online documentation or the ssh_config man page. Some interesting/useful things that you can do include: change the default number of connection attempts, specify local environment variables to be passed to the remote server upon connection, and even the use of * and ? wildcards for matching hosts.

I hope that some of this is useful to a few of you. Leave a note in the comments if you have any cool tricks for the SSH config file; I’m always on the lookout for fun hacks.

There is a great deal of documentation and many posts on Git out there, so this is more of a note to self as I keep forgetting the steps needed to set up a remote repository and doing an initial “push”.

Note the extra import at the beginning, without it Python doesn’t know about MySQLdb’s cursors module. You should also be wary of guessing the order that the items in each row of the DictCursor are returned in. There is no guarantee, for instance, that “columna” will always be the first key and “columnb” the second. When using the DictCursor you should always access values directly by their key. When using the normal cursor class you can access the returned values in sequence (make sure never to use “SELECT *”) as that’s the only way you can associate a value with the column it has come from.